As one of causes of a global warming phenomenon, for example, a greenhouse effect due to CO2 contained in the flue gas from a boiler has been pointed out, and countermeasures thereof have also become an internationally urgent need in protecting the global environment. A source of generation of CO2 extends to the various fields of activities where fossil fuel is combusted, and a demand to suppressing the discharge tends to be further strengthened. Along with this, directed at a power generation apparatus such as a thermal power plant that uses a large amount of fossil fuel, a method of removing and recovering CO2 in a flue gas by bringing the flue gas of a boiler into contact with an amine-based absorbent has been extensively studied.
Since a CO2 absorbent that absorbs CO2 is an amine compound, the degradation and shortening of life of the absorbent due to accumulation of a substance caused by NO2 and SO2 in the flue gas have become a problem.
For that reason, conventionally, there has been a suggestion for reducing a SO2 concentration in the flue gas from a coal combustion boiler and reducing a NO2 concentration in a natural gas flue gas (Patent Literatures 1 and 2).